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This C code provides an interface between YottaDB/GTM and libcurl. I developed it because it was getting to be too hard to maintain a performant HTTP library in M. I specifically needed it to provide all the newest features of TLS support.

The following features in libcurl have been implemented:

  • All HTTP verbs are supported
  • TLS supported - normal; with client certificates (w or w/o passwords); and with addition CA bundles. All TLS versions that curl supports are supported.
  • HTTP Basic Auth support; none others right now.
  • Can send in different mime types
  • Can adjust timeout
  • Can get back output headers
  • Ability to reuse the same connection(s) for multiple HTTP requests


The source code needs to be compiled and installed into an existing GT.M/YDB instance. Right now, you just need to download the repository


After downloading the software, you need to set your gtm_dist environment variable and type make install as root (or can do sudo -E make install) inside the libcurl directory. Here's some sample output:

saichiko:libcurl sam$ sudo -E make install
cc -Wall -O3 -I/usr/local/lib/yottadb-r123-x86_64-debug/ -fPIC   -c -o libcurl_ydb_wrapper.o libcurl_ydb_wrapper.c
cc -o libcurl_ydb_wrapper.o -shared -lcurl
echo './' > libcurl_ydb_wrapper.xc
cat libcurl_ydb_wrapper.xc_proto >> libcurl_ydb_wrapper.xc
cp /usr/local/lib/yottadb-r123-x86_64-debug//plugin
echo '$gtm_dist/plugin/' > /usr/local/lib/yottadb-r123-x86_64-debug//plugin/curl_ydb_wrapper.xc
cat libcurl_ydb_wrapper.xc_proto >> /usr/local/lib/yottadb-r123-x86_64-debug//plugin/libcurl_ydb_wrapper.xc
chmod a-w /usr/local/lib/yottadb-r123-x86_64-debug//plugin/ /usr/local/lib/yottadb-r123-x86_64-debug//plugin/libcurl_ydb_wrapper.xc
echo 'Put this in your env file: '
Put this in your env file:
echo 'export GTMXC_libcurl="/usr/local/lib/yottadb-r123-x86_64-debug//plugin/libcurl_ydb_wrapper.xc"'
export GTMXC_libcurl="/usr/local/lib/yottadb-r123-x86_64-debug//plugin/libcurl_ydb_wrapper.xc"

As it tells you, you need to add an environment variable to your GT.M/YDB install: it's GTMXC_libcurl. The above is a sample; the installer will give you the actual value to put in.

External Documentation

This project relies on libcurl ( While you probably won't need an extra documentation, you may need it if you want to add new features.

M Entry Point Signatures

All the entry points can be invoked as extrinsics functions or as procedures. For example, you can invoke libcurl.init as do &libcurl.init or write $&libcurl.init. Unless indicated with a dot in front of a variable, all parameters are free text values passed by value (except timeout, which is an integer).

libcurl.curl(.httpStatusCode,.httpOutput,"HTTP VERB","URL","PAYLOAD","mime/type",timeout,.output headers)
libcurl.init(),.httpOutput,"HTTP VERB","URL","PAYLOAD","mime/type",timeout,.output headers)
libcurl.addHeader("header: text")
libcurl.clientTLS("path to cert","path to key","key password","path to CA Bundle")


Single GET/Multiple GET

The simplest use case is to use it to make a single GET request.

 n status s status=$&libcurl.curl(.httpStatus,.output,"GET","")

status is the status of the C call, which is always 0 for successful transfers. If you receive more than 1 MB, it will be 255, as GT.M/YDB cannot have a local variable that is greater than 1 MB in length. Any status that's not zero will throw an M error; so realistically, unless you set-up an error trap, you won't capture non-zero statuses.

httpStatus will be 200 for successful connections; and output will contain the output of your operation. You do not have to make an extrinsic call and keep a variable to keep track of the extrinsic output; you can call any operation with a do command; just omit the dollar sign: do &libcurl.curl(...)

If you will make multiple requests to the same host(s), you will be served well (and honestly, that's the main reason I wrote the plugin) to initailize the context, make the connections, and then close the context when you are done, like this:

 n sss,zzz
 d &libcurl.init
 n status s status=$&,.zzz,"GET","")
 d &libcurl.cleanup

Here's a realistic example, against the NLM RxNorm API:

 n sss,zzz,status
 d &libcurl.init
 s status=$&,.zzz,"GET","")
 s status=$&,.zzz,"GET","")
 s status=$&,.zzz,"GET","")
 s status=$&,.zzz,"GET","")
 s status=$&,.zzz,"GET","")
 s status=$&,.zzz,"GET","")
 d &libcurl.cleanup


To do a PUT or a POST, you need to provide a payload, and make sure you use PUT or POST as the HTTP verb. E.g.:

 n sss,zzz
 N CRLF S CRLF=$C(13,10)
 N R S R=$R(123423421234)
 S PAYLOAD(1)="KBANTEST ; VEN/SMH - Test routine for Sam ;"_R
 n status s status=$&libcurl.curl(.sss,.zzz,"POST","",PAYLOAD)

If you need to supply a mime type (as curl defaults to application/x-www-form-urlencoded), pass it in as the parameter after the payload. E.g.:

 n status s status=$&libcurl.curl(.sss,.zzz,"POST","",PAYLOAD,"application/json")


Timeout can be passed as the 7th parameter.

 n status s status=$&libcurl.curl(.sss,.zzz,"GET","",,,5)

Receiving Response Headers

A reference variable can be added as the 8th parameter to receive the headers. Note that they are all together as one string. You need to $piece them off by $C(13,10) to get each individual header.

 n status s status=$&libcurl.curl(.sss,.zzz,"GET","",,,5,.headers)

Sending Custom Headers

To send custom headers, you need to use .init then .addHeader. The header added needs to be the literal string you are sending as a header: so DNT: 1 not "DNT",1. E.g.:

 d &libcurl.init
 d &libcurl.addHeader("DNT: 1")
 n status s status=$&,.zzz,"GET","",,,5,.headers)
 d &libcurl.cleanup

Sending Basic HTTP Auth

You need to call .auth after .init.

 d &libcurl.init
 d &libcurl.auth("Basic","boo:foo")
 n status s status=$&,.zzz,"GET","",,"application/json")
 d &libcurl.cleanup

Other types of authentication are not supported right now.

Using TLS Client Certificates or Adjusting Certificate Bundles

All certificate work is done via .clientTLS. As with other extension methods, you need to call it after calling .init.

To authenticate against a server with a client certificate that does not have a password, call .clientTLS with two parameters representing the certificate and the key. E.g.:

 d &libcurl.init
 d &libcurl.clientTLS("/tmp/client.pem","/tmp/client.key")
 n status s status=$&,.zzz,"GET","")
 d &libcurl.cleanup

If you need to supply a password to unlock the key, pass that as the third parameter; e.g.:

 d &libcurl.clientTLS("/tmp/client.pem","/tmp/client.key","monkey1234")

You can add a CABundleFile as the 4th paramter. I haven't personally tested that; so I don't know how will it work; but I thought it may be useful in enterprise scenarios, where the certificates may all be self-generated.

Error Codes

There are seen only if you call libcurl as an extrinsic function, and trap the M error that is caused when it returns with a non-zero code.

External Dependencies

This one is pretty obvious: This library uses libcurl; and runs on GT.M or YottaDB.

Unit Tests

Running make test will run the Unit Tests. I am having difficulty with TCERT2 running consistently between platforms; it's disabled on Darwin for now but enabled on Linux and Cygwin. Openssl may ask for a password when generating a certificate even when supplied on the command line. In any case, if that test fails for you, you can disable it by changing the @TEST to #TEST.

 ----------------------------- libcurlPluginTests -----------------------------
T1 - curl GET  [OK]   94.516ms
T2 - curl GET
 -------------------------------------------------------------  [OK]  258.718ms
T3 - curl GET
 -------------------------------------------------------------  [OK]  149.587ms
T4 - init, cleanup runs w/o errors----------------------------  [OK]    1.784ms
T5 - do GET  [OK]   70.650ms
TMI - Multiple GETs from Single Domain - Init-----------------  [OK]    1.559ms
TM1 - Multiple GETs from Single Domain - First.---------------  [OK]  163.308ms
TM2 - Multiple GETs from Single Domain - Second.--------------  [OK]   17.811ms
TM3 - Multiple GETs from Single Domain - Third.---------------  [OK]   12.817ms
TM4 - Multiple GETs from Single Domain - Fourth.--------------  [OK]   30.389ms
TM5 - Multiple GETs from Single Domain - Fifth.---------------  [OK]   15.744ms
TM6 - Mulitple GETs from Single Domain - Sixth.---------------  [OK]   64.836ms
TMC - Multiple GETs from Single Domain - Cleanup--------------  [OK]    1.371ms
TPAY - Test Payload...----------------------------------------  [OK]  228.651ms
TPAYMIME - Test Payload with mime type...---------------------  [OK]   95.221ms
TTO - do GET with timeout...--------------  [OK]   71.703ms
THGET - do GET with headers....-----------  [OK]   70.742ms
THSEND - do Send Custom Headers..-----------------------------  [OK]   80.103ms
TB100 - curl 100 bytes of binary data...----------------------  [OK]   86.745ms
TB1M - curl with >1M bytes of binary dataWeb Service return greater than GTM/YDB Max String Size 1048576---------------------  [OK]  825.846ms
TBAUTH - Basic authoriazation...------------------------------  [OK]  175.201ms
TCERT1 - Test TLS with a client certificate no key password

Generating a RSA private key
writing new private key to '/tmp/mycert.key'
Generating a RSA private key
writing new private key to '/tmp/client.key'
Signature ok
Getting CA Private Key
..------------------------------------------------------------  [OK] 1886.440ms

Future Work

At some point I have to stop working and make a release; there are a lot more features that can be added. Here are my top two:

  • Add the ability to get more than 1 MB of data. I think the best way to do that is to save the data to a file and return the path of the file instead of the data.
  • Depending on user demand, add other types of HTTP Authentication. I couldn't vouch for any of the others as I have not used them myself.